Network functions virtualization (NFV) is a network architecture concept that implements specific functions or entire classes of network device functions as building blocks that may be connected, or chained, together to create communication services. These functions are implemented in a virtualized software environment that enables their distribution to and execution on commodity hardware deployed within a network.
NFV relies upon, but differs from, traditional server virtualization techniques such as those used in enterprise level software. A virtualized network function, or VNF, may be implemented via one or more virtual machines running different software and processes, on top of standard network device or server architectures, such as switches and storage systems, or even in a cloud computing infrastructure, instead of having custom hardware appliances for each network function.
The European Telecommunications Standards Institute (ETSI) has developed an NFV initiative that defines a number of use cases that pertain to virtualization of functions currently specified by the Broadband Forum (BBF), such that they can be deployed on commodity infrastructure. The NFV initiative describes basics of use cases pertaining to two nodes/platforms, the residential gateways (RGs) and broadband network gateways (BNGs), amongst the other cases.
The particular cases of RGs and BNGs imposes some new challenges in the design of the VNFs and access to the virtualization infrastructure in order to preserve existing protocols and procedures while permitting the benefits of virtualization to be applied to service delivery. From the point of view of access, this has to do with scale out of what used to be a monolithic network side termination of the access network.
BBF Technical Report (TR)-101 is a proposal based on 802.1ad (QinQ) with extensions. This proposal defines a manner of establishing a session across the access network that supports a multiple tagging models upstream from an access node. The proposal also supports multiple tagging models on customer drops. TR-101 originally focused on digital subscriber line (DSL) access and Ethernet aggregation but has been extended to support passive optical network access (TR-156 & TR-167) and multi-protocol label switching (MPLS) aggregation (TR-178). However all of these recommendations assumed a monolithic border network gateway (BNG) from a single vendor. The decomposition of the BNG function into virtualized network functions and deployment in NFVI significantly alters the scale equation and introduces new challenges as to how load is distributed.